Method of crystal growth by vapor deposition

ABSTRACT

A method for growing elongated rods of silicon or the like by positioning an elongated silicon filament within a reaction chamber, directing the gas from which material is to be deposited over the filament in a direction transverse to the longitudinal axis of the filament at a relatively uniform flow rate along the length of the filament, and while the gas is being directed transversely to the filament, rotating the filament so that all the parts along the surface will be uniformly exposed to the gas.

United States Patent Harrison et ml.

[54] METHOD OF @RYSTAL GRUWTH BY 3,222,217 12/1965 Grabmaier ..117/106VAPUR DEPUSH'HUN 3,341,376 9/1967 Spenke et al. ..1 17/106 3,424,6291/1969 Ernst et al... ..1 17/106 [72] Inventors: James Reneau Harr son,lan James 3,472,684 10/1969 Walther ..1 17/201 Wayne Gilpin, Richardson,both of Tex.

. Primary Examiner-Norman Yudkoff [73] Assignee. lgzrias InstrumentsIncorporated, Dallas, Assistant Examiner Rl T. Foster Att0rneySamuel M.Mims, Jr., James 0. Dixon, Andrew M. [22] Filed: June 5, 1968 l-lassell,Harold Levine, James C. Fails, Melvin Sharp and pp No 73 759 Richards,Harris & Hubbard [57] ABSTRACT [52] [1.5. Cl ..23/294, 23/273 SP,117/106, A method for growing elongated rods of Silicon or the like byInt Cl ggfiggg positioning an elongated silicon filament within areaction e o e o s s l v a I l e I l u [58] new Search 7 301 depositedover the filament in a direction transverse to the 23/294 117/200 l071longitudinal axis of the filament at a relatively uniform flow ratealong the length of the filament, and while the gas is being [56]References Cmed directed transversely to the filament, rotating thefilament so UNITED STATES PATENTS that all the parts along the surfacewill be uniformly exposed to the gas. 2,907,626 10/1959 Eisen et al. ..ll7/107.1 3,004,866 10/1961 Bolton et 31.. 17/107.1 6 911111115, 5Drawing Flaws 3,055,741 9/1962 Maclnnis et al. ..23/273 l6 l5 0 0 I5 0 o28 I3 34 o 1 v a o o u o o 3O 0 o o 26 a 33.,. m/

O O 0 0 D PATENTED JAN? 8 B72 SHEET 1 [1F 2 FIG. 2

INVENTORS W N. 1 w m M m RW s E MMAW A A JJ FIG. 4

ATTORNEY METHOD OF CRYSTAL GROWTH BY VAPOR DEPOSITION This inventionrelates to chemistry, and more particularly, but not by way oflimitation, to methods and apparatus for depositing material from avapor or gas onto a substrate.

In the semiconductor industry, it is common to deposit material from agas onto a substrate for the purpose of forming various electroniccomponents. In some applications the material deposited from the gas isthe same material as that from which the substrate is formed, while inother instances it is a different material from that which the substrateis formed. As an example of the former, in the growth of silicon byvapor deposition techniques, it is common to position an elongatedsilicon filament between two chucks each of which extend through the endof a quartz container within which the filament is placed. A potentialis impressed across the graphite chucks causing a current to flowthrough the filament. The resistance of the filament to current flowelevates the temperature of the filament to a temperature generally inexcess of about l,l C. A gas stream, which may comprise a mixture oftrichlorosilane and hydrogen, is introduced into the quartz chamber andafter flowing along the longitudinal axis of the filament is withdrawnfrom the chamber. The gas stream, upon contacting the hot surface of thesilicon filament, will react to deposit silicon on the filament, thusincreasing the diameter of the filament. The reaction of thetrichlorosilane and hydrogen may be generally illustrated by thefollowing simplified formula:

Gas flow through the quartz cylinder or reaction chamber is usuallycontinued for several hours to increase the diameter of the filament,which may be one fourth inch in diameter upon commencement of thedeposition, to the diameter in excess of 1 inchjWhen the silicon rod hasreached a desired diameter, flow is terminated and the rod is removedfrom the reaction chamber. Usually the material deposited on the siliconfilament will be polycrystalline and therefore must be zone melted toproduce a single crystalline material which is then sliced and furthertreated to produce transistors, diodes and the like. Alternatively, thepolycrystalline rod may be melted in a crucible and a largesingle-crystal rod pulled" from the melt by any ofa variety ofapparatus, such as a Czochralski" puller.

The reaction vessel, usually quartz, within which the deposi tion iseffected can assume various shapes. The vessel may be cylindrical inshape, and the filament mounted concentrically therewithin. The reactionvessel may also be dome shaped with the filaments being supportedtherewithin in a hairpin fashion as illustrated in U.S. Pat. No.3,053,638.

For many applications, it would greatly decrease the time and expense ofpreparing final semiconductor components from silicon slices if theslices were all of a uniform diameter. Before the slices can be ofuniform diameter, the rod from which they are cut must be of uniformdiameter which requires that either the rod as removed from the reactorafter deposition be uniform or that the rod after removal be ground to auniform diameter. Using the deposition techniques, such as describedabove, it is virtually impossible to obtain rods having uniform diameterduring the deposition process. More particularly, it is common that thesilicon rods, after removal from the reactor have a center diameterwhich is about 1.25 times the diameter of the ends of the rod. The rodmust then be ground to remove the excess material between the ends ofthe rod which not only increases the expense of producing semiconductorcomponents but involves a waste of silicon material.

Since, for various reasons, the silicon rods formed in the depositionreactors must be of a minimum diameter, it is necessary to continuedeposition for extended periods of time after the intermediate portionof the rods has reached the required diameter to permit those portionsof the rod near the ends to reach the required size. Thus, more time isconsumed and more reactants are required than would be necessary if thedeposition could be conducted in an environment which was conducive tothe formation of a rod of uniform diameter throughout its length. Thepurity of the finished material would also be improved, as grinding of arod having nonuniform diameter necessarily introduces contaminants whichare undesired.

Silicon rods having nonuniform diameters are believed to be created invarious of the deposition techniques presently being used because thegas from which the silicon is being deposited onto the substrate willchange in composition as it traverses the length of the filament. Theend of the filament positioned near the end of the reaction chamberthrough which the gas is admitted will be exposed to a gas having oneconcentration, while the end of the filament at the opposite end of thereactor will be exposed to a gas of a different composition, since aportion of the gas will have reacted intermediate the ends to depositsilicon along the length of the filament. Also, various countercurrentsof the gas can be created in the reactor during the deposition causingthe gases to be exposed for longer periods of time to certain portionsof the filament than they are to other portions of the filament. lndome-shaped reaction vessel having a gas flow pattern which causes thegas to flow somewhat transverse to the longitudinal axis of thefilaments supported therewithin, such as in US. lPat. No. 3,053,638, thefilaments can grow with an irregular diameter since the concentration ofreactants in the gas will vary along the length of the filament andaround the circumference. Attempts have been made to avoid theseproblems by alternating the points at which the gas is introduced intothe reaction chamber. For example, the gas for a given period of timewill be introduced through one end of a cylindrical reactor anddischarged through the other, after which the flow direction will bereversed for a like period of time. However, such technique does notsolve the problem as the resulting silicon rods continue to benonuniform in diameter requiring that they be ground before zone meltingand slicing.

The method of the present invention may be generally described as animproved method for growing rods of material by depositing material ontoan elongated filament from a gas being circulated over the filament. Themethod includes the steps of suspending the filament within theenclosure and directing the gas over the filament in a directiontransverse to the longitudinal axis of the filament at a flow rate whichis relatively uniform along the length of the filament. During passageof the gas over the filament, the filament is rotated so that all pointsalong the surface will be uniformly exposed to the gas.

The apparatus of the present invention may be generally described as onefor the growing of rods of material by deposition onto an elongatedfilament from gas being circulated over the filament which apparatusincludes a reaction chamber having parallel, foraminous front and backpanels through and between which a gas may flow. A manifold ispositioned over a front foraminous panel for distributing a gas admittedinto the manifold evenly over the surface of the front panel. Chucksextend into the reaction chamber in registering relationship so that anelongated filament can be received therebetween, and the chucks arerotatably mounted relative to the chamber so that the filament may berotated with its longitudinal axis parallel to the front panel. Meansare provided for rotating at least one of the chucks relative to thereaction chamber and thereby the filament. The apparatus preferably alsoincludes a foraminous back panel which is also provided with a manifoldso that the pressure across the back panel will be fairly uniform overthe entire panel.

For a more complete understanding of the present inven tion, referenceis here made to the drawings, in which:

HO. 1 is a perspective view, partially cut away, of one embodiment ofthe apparatus of the present invention;

FIG. 2 is a cross-sectional, elevational view of the apparatusillustrated in FIG. ll;

FIG. 3 is a cross-sectional view taken along line 33 of FIG. 2;

FIG. 4 is a bottom plan view of the apparatus illustrated in in FIGS.11, 2 and 3; and

FIG. 5 is a partial, cross-sectional view of electrodes and a filamentsupported thereby.

The present invention provides a method of growing rods of a materialsuch as silicon, which permits the growth of rods having uniformdiameters throughout their length, thus eliminating the necessity ofgrinding rods of nonuniform diameter. Apparatus suitable for thedeposition from a gas onto a filament for obtaining uniform diameterrods is illustrated in FIGS. 1-5, to which reference is here made.

With particular reference to FIG. 1, a reaction chamber generallyindicated by the reference numeral comprises parallel, foraminous frontpanels 11 and 12 which are joined at their lateral edges to side panels13 and 14 and at their ends with top and bottom plates, only top plate15 of which is illustrated in FIG. 1. Foraminous panels 11 and 12, sidepanels 13 and 14, top plate 15 and the bottom plate are preferablyconstructed of quartz. The apertures 16 in foraminous front and backpanels 11 and 12 are preferably about one-eighth inch in diameter.Reaction chamber 10 is covered by a metal jacket, generally indicated bythe reference numeral 17. Jacket 17, over foraminous front and backpanels 11 and 14, forms manifolds 18 and 19. Manifolds 18 and 19 areprovided with headers 21 and 22, respectively. As particularlyillustrated in FIG. 3, manifolds l8 and 19 define with foraminous frontpanels 11 and 12, respectively, chambers 23 and 24.

Disposed between side plate 25 of jacket 17 and side plate 14 ofreaction chamber 10 is a cooling coil 27, turns of which are alsodisposed between top plate 28 of jacket 17 and top plate 15 of reactionchamber 10. Coil 27 also extends along the opposite side and end of theapparatus. Specifically, coil 27 is diaposed between side plate 26 ofjacket 17 and side plate 13 of reactor 10, and as illustrated partiallyin FIG. 5, coil 27 also is disposed between bottom plate 29 of jacket 17and bottom plate of reaction chamber 10. Coil 27 is provided with inletand outlet connectors 31 and 32, respectively, through which a coolingfluid, such as water, may be circulated for cooling side plates 13 and14 and top plates 15 and 20 of reaction chamber 10.

As illustrated by FIG. 3, a plurality of elongated filaments 33 aresupported within reaction chamber 10 parallel to the foraminous panels11 and 12. The filaments 33 are supported within reaction chamber 10 bya set of top chucks 34, each of which is in registering alignment whichone of the corresponding set of bottom chucks 35. With reference to FIG.5, which illustrates one of the bottom chucks 35 and the manner in whichit is supported within the apparatus of FIG. 1, each of the chucks 35,which may be constructed of graphite or the like, passes through bottomplate 29 of jacket 17 and bottom plate 20 of reaction chamber 10. Chucks35 are rotatably mounted relative to jacket 17 and reaction chamber 10by a circular bearing 36 which engages a teflon insulating sleeve 37surrounding a portion of chuck 35. Each of the chucks 35 is providedwith a square recess 38 which receives there within the square shapedend 39 of filament 33 so that rotation of chuck 35 will cause rotationof filament 33. The opposite end 41 of filament 33 is also provided withsquare shoulders for receipt within the square recess 42 of the upperregistering chuck 34. Chucks 34 and 35 are spaced from each other asufficient distance to leave sufficient room within recess 42 forfilament 33 to expand in a longitudinal direction when heated. To permitrotation of graphite chucks 35, each has a filled teflon ring gear 43press fit around sleeve 37.

As particularly illustrated in FIG. 4, each of the gear rings 43 mountedon chucks 35 is engaged with an adjacent gear 43 so that rotation ofadriven gear wheel 44 will effect simultaneous rotation of gears 43through a coupling gear wheel 45 which engages one of the gears 43 anddrive gear 44. As illustrated in FIG. 2, drive gear 44 is driven by aconventional electric motor and transmission assembly 46.

To permit communication of a current through each of the filaments 33,each of the chucks 35 is provided with a radially enlarged portion 47which forms a top beveled circumferential surface 48 and a bottombeveled circumferential surface 49. Engaging the radially extendingportion 47 of graphite chuck 35 is an electrode, generally indicated bythe reference numeral 51. Electrode 51 comprises a top ring 52 having aradially relieved surface 53 at its inner diameter which mates with thetop beveled circumferential surface 48. Electrode 51 also includesbottom ring 55 having a radially relieved surface 56 at its innerdiameter which engages bottom beveled circumferential surface 49 ofchuck 35. The top ring 52 and bottom ring 55 are maintained in abutmentand supported by a mounting sleeve 57. Mounting sleeve 57 is providedwith a conventional adjustment, not illustrated, for radially enlargingor compressing ring 57. Ring 57 is also provided with a coupling 58 forattachment of electrical cable 59 thereto.

As illustrated in FIG. 5, top circumferential surface 48 and radiallyrelieved surface 53 define an included angle with the centerline ofchuck 35 which is less than the included angle which bottomcircumferential surface 49 and radially relieved surface 56 define withthe same line. Thus, when rings 52 and 55 are radially compressed bymounting sleeve 57, the bottom ring will exert a greater resultant forceupwardly on beveled surface 49 than ring 52 will exert downwardly onsurface 48. The net upward force tends to maintain chuck 35 in theposition illustrated in FIG. 5 and therefore assure that an effectivegas seal is maintained between sleeve 37 and bottom plate 20 of reactor10.

The structure of the top of the apparatus illustrated in FIG. 1 isidentical to the structure of the bottom but, of course, oriented in adifferent direction. Specifically, each of the gra phite chucks 34which, like chucks 35, will be urged inwardly by the electrodes attachedthereto is mounted to one of a series of ring gears 61, which, asillustrated in FIG. 2, intermesh identical to gears 43 and are driven bya coupling gear 62 mounted on shaft 63 which also carries coupling gear45. Coupling gears 62 and 45 are of the same diameter as are gears 61and 43, thus chucks 34 and 35 are rotated at the same speed. Each of thetop chucks 34 is also, through an electrode 64, in electricalcommunication with one of the electrical cables 65, and the bottomchucks 35, though an electrode 51 is in contact with one of the cables59. Each of the registering sets of chucks 34 and 35 is, through therespective electrodes 64 and 51, connected across a common electricalenergy source so that substantially the same identical current flow willbe established through each of the filaments 33 within the reactionchamber 10.

In operation, the apparatus described above may be used to practice themethod of the present invention. More particularly, silicon filaments 33may be positioned between graphite chucks 34 and 35 by removing thebrace, not illustrated, supporting bottom electrodes 51 permittinggraphite chuck 34 to be removed from the apparatus 10. Silicon filaments33 are then inserted in the chucks 35 and the chucks reinserted into theapparatus. An operator can assure that the filaments 33 are engaged withthe top chucks 34 by viewing filaments 33 as they are inserted throughclear quartz sight glass 30 provided in side plate 25 of the jacket 17.Once the filaments are inserted, and the brace supporting the electrodes51 is reconnected, reaction chamber 10 is flushed with nitrogen andsubsequently with hydrogen gas admitted to manifold 18 through headers21. Hydrogen entering headers 21 will be distributed within chamber 23formed by manifold 18 after which it will flow through apertures 17 inforaminous panel 11, transverse to the filaments 33. The gas will thenexit through apertures 16 in back foraminous panel 12, and will exit thechamber 24 formed by manifold 19 behind back panel 12 through header 22.After reaction chamber 10 has been flushed with hydrogen, thetemperature of the filament 61 is elevated to the desired temperature,for example I,l00 C., if the filament is silicon, by impressing apotential between the top electrodes 64 and bottom electrodes 51. Whenthe filaments 33 have reached the desired temperature, a gaseous streamcontaining reactants is circulated through headers 21. If the filamentis silicon, for example, a mixture of trichlorosilane and hydrogen in aratio of 5:95 (by volume) could be admitted to headers 21. In chamber23, the gas is distributed over the foraminous panel 1] to maintain afairly uniform pressure across the face of panel 11 so that the gas flowthrough the apertures 16 will be at a substantially uniform rate thusexposing each of the filaments 33 to approximately the same amount ofgas along the entire length of the filaments 33. The gas, since ittraverses reaction chamber transverse to the longitudinal axis of eachof the filaments 33 exposes the entire length of each of the filaments33 to a gas of the same concentration, thus avoiding creation ofsegments of the filaments which are larger in diameter than those ofother portions of the filament. The gas, which as described, may betrichlorosilane and hydrogen reacts in reaction chamber 10 to depositsilicon on filaments 33, and after reacting is discharged throughforaminous back panel 12 into chamber 24 and out through headers 22. Dueto the manifold 19, the gas pressure across the foraminous back panel 12will be approximately equal at all points, thus avoiding channeling ofgas flow through reac tion chamber 10, further insuring that the entirelengths of each of the filaments 33 are exposed to approximate uniformquantities in a gas which is of a fairly constant concentration alongthe entire length of filament 33.

To insure that the filaments 33 grow in a uniform manner, the filamentsare rotated by actuation of motor and transmission assembly 46, whichrotates the elements at the rate of l revolution per minute or less formost application. Since the filaments may become quite plastic under theinfluence of the high temperatures, the gear assemblies provide an equaland simultaneous rotary force to both ends of filaments 33, thusminimizing any stress which may be created by rotation by impartingrotary force to only one end.

When the desired amount of material has been deposited on filament 33,which may be determined by inspection through sight glasses 30, the gasflow may be terminated and the rods of material removed in a reversemanner from which filaments 33 were installed.

With the present invention, it is possible to grow rods of uniformdiameter throughout their length, thus avoiding the problems created bythe necessity of grinding away excess material from rods of nonuniformlength.

The invention may be used in the growing of various materials includingeither single crystal or polycrystalline silicon or germanium, or informing epitaxial layers of various materials on substrates of yetanother material. Various types of foraminous panels may be used todistribute the gas flow evenly, including a quartz frit material, andthe expression foraminous" is used to include various porous materialsthrough which gas flow may be effected.

While rather specific terms have been used to describe an embodiment ofthe apparatus of the present invention and the method of the presentinvention, these expressions are not intended, nor would they beconstrued as limitation upon the invention as defined with the followingclaims.

What is claimed is:

1. An improved method for the chemical vapor deposition of a materialonto an elongated hot filament from a decomposable gas passed over thesteps of:

suspending the filament within an enclosure;

directing the gas into the enclosure and over the filament in adirection transverse to the longitudinal axis of said filament at a flowrate and in a manner which is substantially uniform along substantiallythe entire length of said filament;

withdrawing the resulting off gases from said enclosure in a directiontransverse to the longitudinal axis of said filament at a flow rate andin a manner which is substantially uniform along substantially theentire length of said filament; and

rotating the filament so that all points along the surface of thefilament will be uniformly exposed to the gas.

2. The method of claim 1 which is further characterized by the filamentbeing suspended in a vertical position and the gas being directedtransversely over said filaments being introduced through a firstforaminous panel parallel to the longitudinal axis of the filament.

3. The method of claim 1 which is further characterized by theimpartation of simultaneous rotary force to both ends of said filamentthereby minimizing the creation of stresses in the filament.

4. The method of claim 1 wherein the gas flowing transversely over saidfilament is introduced through a first foraminous panel and afterpassing by said filament passes through a second foraminous panel.

5. An improved method for growing rods of semiconductor material bydepositing said material onto an elongated hot filament from adecomposable gas circulated over the filament, which comprises the stepsof:

introducing the gas into a first manifold to distribute the gas withinthe manifold and thereby maintain a substantially uniform pressurewithin the manifold,

passing the gases from said first manifold through a first foraminouspanel positioned parallel to the longitudinal axis of the filament tothereby direct the gas transversely of the longitudinal axis of thefilament, and

rotating the filament so that all points along the surface thereof willbe uniformly exposed to the gas being introduced through the firstforaminous panel, passing said gas after contact with said filamentthrough a second foraminous panel also generally parallel to thelongitudinal axis of said filament, and directing the gas passingthrough the second foraminous panel into a second manifold formaintaining a fairly uniform pressure across the second foraminouspanel.

6. The method of claim 5 in which a simultaneous rotary force isimparted to both ends of said filament to minimize creation of stressesin said filament.

2. The method of claim 1 which is further characterized by the filamentbeing suspended in a vertical position and the gas being directedtransversely over said filaments being introduced through a firstforaminous panel parallel to the longitudinal axis of the filament. 3.The method of claim 1 which is further characterized by the impartationof simultaneous rotary force to both ends of said filament therebyminimizing the creation of stresses in the filament.
 4. The method ofclaim 1 wherein the gas flowing transversely over said filament isintroduced through a first foraminous panel and after passing by saidfilament passes through a second foraminous panel.
 5. An improved methodfor growing rods of semiconductor material by depositing said materialonto an elongated hot filament from a decomposable gas circulated overthe filament, which comprises the steps of: introducing the gas into afirst manifold to distribute the gas within the manifold and therebymaintain a substantially uniform pressure within the manifold, passingthe gases from said first manifold through a first foraminous panelpositioned parallel to the longitudinal axis of the filament to therebydirect the gas transversely of the longitudinal axis of the filament,and rotating the filament so that all points along the surface thereofwill be uniformly exposed to the gas being introduced Through the firstforaminous panel, passing said gas after contact with said filamentthrough a second foraminous panel also generally parallel to thelongitudinal axis of said filament, and directing the gas passingthrough the second foraminous panel into a second manifold formaintaining a fairly uniform pressure across the second foraminouspanel.
 6. The method of claim 5 in which a simultaneous rotary force isimparted to both ends of said filament to minimize creation of stressesin said filament.